For many years, various procedures have been proposed for solving the difficult problem of feeding fine coal into a pressurized zone, such as the interior of a gasifier, without encountering severe apparatus costs and maintenance problems or water-induced losses of thermal or chemical efficiency. The commonly employed lock-hoppers are known to be both expensive to manufacture and difficult to maintain. And, the injecting of pressurized aqueous slurries of coal fines is known to provide a thermal burden in a gasifier.
U.S. Pat. No. 3,182,825 suggests avoiding the inefficiency of lock-hoppers by centrifugally pumping pulverized dry coal into the interior of a gasifier.
U.S. Pat. Nos. 3,957,460; 4,153,427 and 4,244,706 suggest pressurizing aqueous slurries of coal and then partially combusting some of the coal in order to provide relatively dry coal at the pressure of a hydrotreater or gasifier.
U.S. Pat. No. 4,209,304 suggests extruding moist coal into hot gas, drying the resultant dispersion, and then feeding the dried dispersion into a gasifier.
Organic solvents, particularly those which are miscible with both oil and water, are known to be useful for dewatering coal fines. U.S. Pat. No. 3,327,402 by T. J. Lamb, E. L. Mitch and W. C. Naumann describes a process of dewatering coal to a selected degree by contacting wet coal fines with an organic solvent which is at least 10% miscible with water and then removing at least a substantial portion of the water-solvent solution from the coal particles. U.S. Pat. No. 4,185,395 describes an organic solvent-aided process for dewatering raw brown coal to form a relatively water-free slurry of raw brown coal fines in a liquid organic solvent.